I have Linux Virtual machine (ubuntu 12.04) installed on my Mac OS.
On my terminal,
firstname.lastname@example.org:~$ su password: su : Authentication failure email@example.com:~$ ls -lth /bin/su -rwsr-sr-x 1 root root 36K Sep 12 2012 /bin/su
But the following works:
firstname.lastname@example.org:~$ sudo ls [sudo] password for user: (....lists the directories) email@example.com:~$ sudo -s [sudo] password for user: firstname.lastname@example.org:~#
Hence the question is,
sudo -s works and logs in as root, while
su results in authentication failure.
I typed the passwords correctly each time.
sudo ls works